The 21-year-old Australia international has been generating plenty of transfer speculation, with one £600,000 bid from Championship new boys Rotherham United knocked back.
Cooper is aware that the rumours are likely to continue throughout the summer window, but he is adamant that a man snapped up from Tottenham Hotspur in September 2013 is going nowhere.
He said after a 5-2 pre-season friendly victory over Petersfield: "He's not going.
"And I don't know if we would sell him. I don't think there's any pressure.
"We have been a selling club but I think the way Lee (Power, chairman) is doing it is that if we are sustainable we don't have to sell players.
"With all due respect to Rotherham, I don't think Mass would go there.
"It was a fantastic offer, but I think he's worth more than that."
Meanwhile, Cooper has confirmed that Swindon have taken Oldham Athletic midfielder Anton Rodgers, son of Liverpool boss Brendan, on trial.
He said of the 21-year-old: "We're just having a look at Anton.
"He's free from Oldham and Luke (Williams, assistant coach) has worked with him before. He said he's worth having a look at."